Quick pinion angle question

The issue is you can’t just use the ground as a reference point. Pinion angle uses the relationship of the end output shaft of the transmission to the pinion yoke. So say the end of output shaft is 90 degs to the ground and your pinion yoke is 4 degs down. Then you move the back of the car down. The transmission is no longer 90 degs. You will lose some of the pinion down angle. The end of the output shaft and the yoke face will come closer to being parallel. How much? You will have to measure